Structure and antitumor activities of the water-soluble polysaccharides from Ganoderma tsugae mycelium

Six water-soluble polysaccharides coded as GTM1 to GTM6 were extracted sequentially from the mycelium of Ganoderma tsugae with 0.2 M sodium phosphate buffer solution at 25, 40, and 80 °C, water at 120 °C, 0.5 M sodium hydroxide at 25 and 65 °C. The chemical structures were determined by using IR, EA, GC and 13C NMR. The weight-average molecular mass (Mw) was characterized by size exclusion chromatography combined with laser light scattering (SEC-LLS). The results indicated that the samples GTM1 and GTM2 were heteropolysaccharide-protein complexes with the protein content of 13.5 and 20.1%, and apparent-mean Mw of 62.8×104, 81.8×104, respectively. GTM3 and GTM4 contained (1→3)-β-d-glucans and (1→4)-α-d-glucans, while GTM5 and GTM6 were mainly a (1→6)-branched (1→3)-β-d-glucan. Two peaks were found in the SEC patterns of the four samples GTM1 to GTM4, representing fractions 1 composed of branched (1→4)-α-d-glucan with high Mw and fraction 2 composed of galactose, glucose and mannose with relatively low Mw. With the progress of isolation, the content of fraction 2 decreased from 90.2 to 57.1%, accompanying with enhancing antitumor activity. The polysaccharides GTM1, GTM2 and GTM3 had significantly higher antitumor activity against solid tumor Sarcoma 180 with the inhibition ratio beyond 50%. The results suggested that the effects of the moderate content of galactose and bound protein, as well as relatively lower Mw, on the improvement of antitumor activities of polysaccharides could not be negligible.